The present invention relates generally to amplified speakers and, more particularly to an active sub-woofer speaker system.
Sub-woofer speaker systems are designed to reproduce the lowest bass frequencies in music and sound, such as audio frequencies below 35 Hz. These low frequencies cannot be reproduced by conventional smaller woofers so larger audio drivers or speakers cones having a diameter of ten (10) inches or more are typically used in sub-woofer speaker systems. Sub-woofers are typically used with stereo amplifiers or home entertainment systems to give an enhanced, realistic listening experience in which these lower frequencies can be heard and felt by the listener.
Sub-woofers are designed to be either powered or passive. In the powered or active variety, the sub-woofer system has a built-in power amplifier to drive the sub-woofer speaker. Typically, sub-woofer systems have the power amplifier and its associated power supply mounted directly on or within the enclosure of the speaker system. Powered sub-woofers typically find use in applications where a local amplifier of a stereo or home entertainment system is limited in its output power and cannot drive the sub-woofer to its full efficiency. The powered sub-woofers therefore increase the capability of the local audio source amplifier by providing remote amplification of audio signals generated by the audio source through the use of the built-in power-supply and amplifier at the speaker.
Passive sub-woofers, on the other hand, do not have built-in power supplies or amplifiers, but rather rely on the amplifier of the audio source to drive the sub-woofer audio driver. Therefore, passive sub-woofers are generally not able to produce the same sound level as powered sub-woofers due to the limited output power of most conventional stereo amplifiers.
Typically, powered or active sub-woofers include a class-AB audio power amplifier to drive the speaker. However, class-AB audio amplifiers generally have a relatively low efficiency so a significant amount of input power to the amplifier is wasted as heat. Massive aluminum heat sinks are therefore used to keep the class-AB audio amplifier cool which leads to increased size, weight and cost of such amplifiers. Additionally, powered or active sub-woofer speaker systems typically use conventional E-I laminated transformers as a power supply to drive the audio amplifier. However, E-I laminated transformers tend to be relatively large due to their relative inefficiency and therefore preclude the use of conventionally powered sub-woofer speaker systems in closely confined spaces such as a house wall cavity.
Therefore, there is a need for an active or powered sub-woofer that is adapted to be readily mounted in a closely confined space for reproducing low frequency audio information from an audio source.
The present invention overcomes the foregoing and other shortcomings and drawbacks of sub-woofer speaker systems heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The sub-woofer speaker system of the present invention is designed to be mounted in a closely confined space such as a house wall cavity, ceiling, floor or other low profile enclosure. In accordance with the principles of the present invention, the active sub-woofer speaker system includes a power supply circuit, an audio amplifier circuit powered by the power supply circuit, and a sub-woofer audio driver that is driven by the audio amplifier circuit. Low frequency audio signals are coupled from an audio source, such as a stereo amplifier or home entertainment system, to the audio amplifier circuit of the sub-woofer speaker system. The audio signals are amplified by the audio amplifier and coupled to the sub-woofer audio driver for reproduction of the low frequency audio information within a listening area. The sub-woofer audio driver preferably has a diameter of about ten (10) inches to give an enhanced, realistic listening experience to the listener.
The power supply circuit of the sub-woofer speaker system includes a toroidal power transformer coupled to a rectifier and filter circuit. The toroidal power transformer typically has a minimum efficiency of about 90%, and negligible leakage inductance and stray capacitance. Due to its relatively high efficiency, the toroidal power transformer is significantly smaller than conventional E-I laminated transformers.
The audio amplifier circuit includes an audio preamplifier circuit having an audio input adapted to be coupled to the audio signal source and an audio output coupled to a class-D audio amplifier. The class-D audio amplifier typically has a minimum efficiency of about 90%. Due to its relatively high efficiency and minimal heat loss, the class-D power amplifier is significantly smaller and lighter than conventional class-AB audio amplifiers. Each of the audio preamplifier circuit and class-D audio amplifier circuit is coupled to the rectifier and filter circuit for receiving DC power therefrom. A sub-woofer audio driver is coupled to an audio output of the class-D amplifier and is operable to produce low frequency audio information in response to audio signals coupled to the preamplifier circuit from the audio source. Preferably, the power supply circuit, audio amplifier circuit and the sub-woofer audio driver have a low profile, such as a depth of less than about four (4) inches, so the sub-woofer speaker system may be readily mounted in a closely confined space such as a house wall cavity, floor, ceiling or other low profile enclosure.
It will be appreciated that the minimum 90% efficiency of the toroidal power transformer with its negligible leakage inductance and stray capacitance permits a smaller power transformer to be used in the sub-woofer speaker system of the present invention over the conventional E-I laminated power transformers of the past. Moreover, it will also be appreciated that the minimum 90% efficiency of the digital class-D audio amplifier with its minimal heat loss permits a smaller and lighter audio amplifier to be used in the sub-woofer speaker system of the present invention over the conventional class-AB audio amplifiers of the past. The combination of the toroidal power transformer, class-D audio amplifier and sub-woofer audio driver, each having a low profile of less than about four (4) inches, permits the sub-woofer speaker system of the present invention to be readily mounted in a closely confined space for reproducing low frequency audio information from an audio source.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.